1. Field of the Invention
This invention relates generally to mooring arrangements for offshore floating facilities such as floating production, storage and offloading vessels (FPSO). In particular the invention relates to a riser arrangement and method for its installation by which hydrocarbon fluids from subsea wells are transferred to the vessel. Still more particularly the invention relates to a method of installing a riser system in a turret-moored vessel.
2. Description of the Prior Art
Prior riser systems have included flexible risers which extend from sea-bed wells or manifolds to the interior of a mooring turret of a FPSO for connection to a fluid swivel mounted on the turret. With deepwater subsea production systems it is advantageous to provide a rigid pipeline for connection at the seabed for connection to subsea wells and manifolds, yet a flexible riser is needed at the vessel for coupling to the turret.
U.S. Pat. No. 5,639,187 discloses a marine riser system which combines rigid (steel catenary) risers with flexible flow lines. The steel catenary risers extend from the sea floor in a gentle catenary path to a large submerged buoy positioned at a depth below the turbulence zone of the sea. Flexible risers are connected to the rigid steel risers at the submerged buoy and extend upwardly to a floating platform or vessel used as a surface production and/or storage and offloading facility.
There remains an unsolved problem of providing an arrangement and method for its installation of a combined rigid/flexible riser to a turret of a turret moored FPSO.